Dual concentric drill pipe systems are particularly useful for drilling situations wherein the conservation of drilling fluid (e.g., mud or water) is important. A system for reverse circulation dual tube drilling is disclosed in Henderson U.S. Pat. No. 3,208,539.
In conventional circulation, single tube drilling systems, drilling fluid is pumped down the drill pipe to the bit, and returns to the surface in the annular space between the drill pipe and the hole wall (the hole annulus). In reverse circulation dual tube system the drilling fluid is pumped down the annular space between the inner and outer tubes (the pipe annulus) and returns to the surface through the inner tube. Thus, loss of drilling fluid is minimized. Reverse circulation dual tube drilling is a particularly valuable technique in connection with the drilling of water wells, especially in remote or arid regions, where water or other drilling fluid is difficult or expensive to obtain.
The development and cleaning of screened water wells is a significant aspect of water well technology. Prior art systems and techniques for the development of water wells are described in a publication of the United States Army dated August, 1957, "WELLS" (Department of the Army Technical Manual TM5-297). These techniques include surging with plungers, open and closed-well methods using compressed air, backwashing, and the like. A common element of the prior art methods involves agitation of the formation water in the vicinity of the well screen so as to clean the screen and surrounding gravel of small particles and draw those particles into the well. The particles and dirty water are then removed from the well, either by conventional bailing, or by airlift using an airline and drop pipe.
Such prior art techniques suffer several deficiencies. It is usually not possible to employ the drill pipe which was used to drill the well as part of the development system; separate airlines and eductor pipes are required. In addition, in compressed air systems, compressor requirements are often too high, and development proceeds at an inefficient rate.